1. Field of the Invention
The present invention relates to apparatus and method for electrical stimulation of muscles. In particular, the present invention relates to a programmable muscle stimulator which automatically reproduces a desired regimen of functional electrical stimulation.
2. Description of the Prior Art
Functional electrical stimulation (FES), which sometimes in a more restricted sense is called neuromuscular stimulation (NMS), is a technique of causing muscles to contract by means of an electrical current. FES is typically used therapeutically when there is a lack of neuromotor faculty, or when muscles which have been weakened or damaged by disease or trauma can benefit from a program of enforced contractions akin to voluntary exercise. In some cases, FES can be used in lieu of or complementary to exercise to strengthen an athlete's muscles. In addition, FES can be used prosthetically when voluntary motor ability is irretrievably lost, such as in certain forms of paralysis.
Muscle stimulators of various types have been developed to accomplish FES. A typical muscle stimulator consists of an electrical pulse generator and one or two pairs of electrodes (depending upon whether the pulse generator has one or two output channels). The electrodes are placed in appropriate locations on the skin, and electrical pulse trains from the pulse generator are applied transcutaneously to produce a contraction of muscles or groups of muscles. The effectiveness of the contraction is determined visually by the clinician, or by the patient himself.
The typical muscle stimulator of the prior art has controls which allow the clinician or the patient to select a stimulation regimen which is best suited for the particular purpose. In general, the controls permit selection of the pulse repetition rate (i.e. the number of pulses per second) and the pulse intensity (i.e. the amplitude, the pulse width or both). Most muscle stimulators also have a "time on" control which determines a contraction time and a "time off" control which determines a relaxation time. The clinician sets these controls to define a succession of contraction/relaxation cycles which the clinician believes is best for the desired purpose. Normally, the relaxation time is longer than the contraction time. For example, in a typical FES regimen the "time on" control may be set for a contraction time of about ten seconds, and the "time off" control may be set for a relaxation time of about twenty-five seconds.
Most muscle stimulators used for FES also include a "ramp up" control which selects a fraction of the contraction time during which the intensity of the pulses increases gradually. This prevents a sudden shock to the patient at the onset of the contraction time, and makes the contraction more naturally "physiological". In some cases, the muscle stimulator includes both a "ramp up" control and a "ramp down" control so that the slope of the pulse intensity at both the onset and the termination of the contraction time can be selected by the clinician.
When commencing the application of FES for any of the purposes described above, the clinician normally sets the stimulator to a "CONTINOUS" mode (which is defined as infinite "time on", zero "time off", and no ramp times) and also selects a pulse repetition rate. After placing the electrodes optimally on the patient's skin, the clinician proceeds to cause a contraction to occur by gradually increasing the intensity setting of the intensity control from a zero setting to a setting which produces a maximum contraction. The clinician then determines (by prior knowledge and intuition) suitable "time on", "time off", "ramp up", and "ramp down" settings. Next, the clinician submits the patient to a session at the selected regimen, and observes the effect of that regimen on the patient. Often the clinician adjusts one or more of the control settings and continues to observe the effects on the patient until a desired regimen is achieved. The patient may then be asked to continue sessions at home using the same regimen. This requires that the patient remember all of the control settings and/or make certain that none of the settings are disturbed.
There is a continuing need for improved muscle stimulators which are easier for both the clinician and the patient to use. In particular, there is a continuing need for a muscle stimulator that saves the clinician (and the patient) the laborious steps which have been performed in the past in order to arrive at a desired FES regimen.